Its most likely due to 4 hours of normal use, IE, playing music, watching videos, surfing the net, playing games, etc. 36 hours of nothing but music playing is possible but not many use it just like that.

i turn my brightness down a lot when i don't need it to be bright, also turn off wifi when you're using the iPod without wifi cause i use mine in school sometimes :x and my school wifi is password protected and my ipod drains the battery searching for other networks w/o passwords

- 128Kbps AAC files encoded manually and also some downloaded from iTunes (kinda weird since one would think the company is just that - one company, but whatever)
- full charge on the battery
- volume at 50%
- playback of music only, I believe they simply start the Music player, tap Songs, tap Shuffle and leave it alone from that point on but the Shuffle thing might be inaccurate, on a Flash-based device the seek times don't consume battery life like they would with a hard drive based iPod
- Wi-Fi is off, in fact everything that's "automated" is off
- after 10-15 seconds of the last tap, the LCD and backlight turn off and then they never touch it again till their test equipment says "It's dead, Steve..." or whatever

So in reality, if you got close to do that sort of usage, you'd get 20+ hours of battery life just playing music perhaps even up towards 30 or even a bit over that I believe. But if you switch songs manually, each time you do it that fires up the LCD and backlight and wham, another chunk of battery life is gone, etc. Maybe sometime someone will find a way to remap the Volume buttons on the side to Next and Previous for skipping songs without turning on the display; I have no need for the volume controls because my earclips have a volume control inline that works fine.

Push Play and leave it alone and you'll get a lot of battery life with music. Videos, basically you're looking at 1/6 of the claimed music time, so 36 for audio, 6 for video, and just keep dividing that down based on usage. If you used a lot of manual playback/switching of songs, used the volume controls on the side to alter settings, etc. you're going to take a battery life hit, but it still seems to work out to video playback being about 1/6th of the possible music only battery life.

And of course, encoding bitrates for audio and video factor into this also. Low bitrate video files (like 500 Kbps or something) will not use nearly as much battery as 1500 Kbps (the max) would. Brightness, Wi-Fi, all that extra fluff just kills it.

If you have a Jailbroken 1st gen iPt and you install OpenSSH or some other SSH server on it, that will kill the battery life dramatically fast if you don't disable/turn off that SSH service when it's not in use. It'll force the Wi-Fi service to stay active even if you're not using it, so that's Wi-Fi + SSH server = dead battery really damned fast. It's a well known battery killer, so keep it in mind.

Hopefully the 2nd gen iPt (and iPhone 3G) will get a Jailbreak soon and we'll have fun all over again...

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